Not an exact number, here's the relevant portion of the email verbatim.

A lot of you might remember that about two years ago, I created a series called Horace and Pete (still available at louisck.net). I paid for that show myself. When I did it, I told myself that I was parting with the money forever. It wasn’t an investment. It was a 4.5 million dollar grant to the "Make whatever the fuck I want" Foundation.
By that approach, I was able to make and roll out the show exactly the way I saw it, the way I wanted the audience (you) to see it, without any concern for commerce or profit.

In the end, the show made all the money back and more (with zero advertising) through website sales, and through licensing it to HULU, I was able to actually make a sizable profit for me and the actors and some of the crew, who own a piece of the show. That was a pretty good result.
So this year, I decided, I got the money back, I can throw it away again. This time to the "Make a Black and White Movie about a Shitty Father foundation.”

According to the email he sent out a couple weeks ago he took the money he got from licensing Horace and Pete to Hulu (as well as direct online sales on his site) and made I Love You, Daddy with it. I don't know if he completely financed it himself but that would make one think he put some serious money into it.